A study of air quality in six US cities reports that fine particulate air pollution is linked with death from cardiovascular disease and possibly lung cancer, and that the overall death rate decreases when pollution decreases. These results were published in the American Journal of Respiratory and Critical Care Medicine.

Fine particulate air pollution is pollution that consists of tiny particles no larger than 2.5 µm (a µm is one millionth of a meter) in diameter. These very small particles tend to cause more health problems than larger particles because they can penetrate further into the lungs. Sources of fine particulate air pollution include combustion from motor vehicles and power generation.

Several previous studies have linked high concentrations of fine particulate air pollution with an increased risk of death. To explore the extent to which reductions in air pollution reduce death rates, researchers evaluated information from the Harvard Six Cities Study.

This study assessed the levels of fine particulate air pollution in six US cities: Watertown, MA; Kingston and Harriman, TN; St. Louis, MO; Steubenville, OH; Portage, Wyocena and Pardeeville, WI; and Topeka, KS. Study participants from each city were enrolled into the study between 1974 and 1977, and their health status has been assessed over time.

Air pollution levels and death rates were assessed for two different time periods: 1974-1989 and 1990-1998.

  • During both time periods, higher levels of fine particulate air pollution were linked with a higher overall death rate as well as a higher rate of death from cardiovascular disease. There was also some suggestion of an increased risk of death from lung cancer.
  • Air pollution levels dropped over time in all six cities. The decline in pollution was most dramatic in those cities that had the highest levels at the start of the study.
  • Overall death rates dropped as air pollution improved. The decline in the overall death rate appeared to be due to a decline in deaths from cardiovascular and respiratory disease.
  • As air pollution improved, there was no evidence of a decline in lung cancer deaths. Lung cancer is likely to be less reversible than cardiovascular or respiratory disease. In addition, lung cancer takes many years to develop, and may not be as responsive to recent changes in exposure.

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The researchers conclude that “These findings suggest that the mortality effects of long-term air pollution may be at least partially reversible over periods of a decade.”

Reference: Laden F, Schwartz J, Speizer FE et al. Reduction in Fine Particulate Air Pollution and Mortality: Extended Follow-Up of the Harvard Six Cities Study. American Journal of Respiratory and Critical Care Medicine. 2006. 173:667-672.

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